1. Field of the Invention
The present invention relates to the field of structural lightweight concretes and mortars and more particularly to structural lightweight concrete or mortar compositions, to their process of manufacture and to the structural concretes or mortars thus obtained, as well as to their use as self-placing concrete.
2. Description of the Related Art
For several years, for better insulation of buildings, a search has been under way to produce concretes or mortars having low thermal conductivity. To this end, mortar compositions have been developed which include air-entraining adjuvants, a high air content making it possible to enhance the insulating thermal performance of the mortar, and/or compositions including light aggregates, such as pumice, expanded clays or expanded schists, exhibiting a high porosity which confers an insulating nature on the material.
However, this weight-reduction must not be made to the detriment of a reduction in the strength of the concrete or mortar and in particular of its compressive strength, which has to be at least 25 MPa after 28 days.
The difficulties increase during the preparation of concretes, when it is desired to increase their fluidities while preventing the phenomenon of bleeding and the segregation of the aggregates. These disadvantages are amplified in the case of self-placing concretes, for which a high fluidity is required.
Furthermore, the mechanical strength properties can be further affected by the replacement, for the purpose of improving the thermal performance of the material by reducing its density (and consequently its thermal conductivity), of all of the conventional aggregates (of high density) by lightweight aggregates, for example of expanded type.